1. Field of the Invention
The present invention relates to devices for feeding sheets singly from a stack. More particularly, the present invention relates to such sheet feeding devices that can be adjusted to feed various sized sheets.
2. Description of the Prior Art
Devices for feeding sheets singly from a stack have long been necessary in machines such as facsimile machines and copying machines for both originals and copying paper. Such devices include a roller having a friction surface for drawing the sheets from the stack. In order to maximize the friction, the roller has been made as long as the maximum sized sheet to be drawn. A problem has been encountered with such a long roller in that the radii of portions of the roller changes over time. Specifically the radius at each end becomes greater than the radius at the center. This results in loss of friction between the roller and the sheets, thus skewing the sheets.
To overcome this problem, the length of the roller has been reduced so that the radius cannot vary as much.
In copying and facsimile machines, sheet feeding devices have generally included a platform on which the stack of sheets is placed and guides for positioning the stack on the platform. To adjust for sheets of various sizes, it has been customary that the guides be adjustable. In fact, the movement of the guides is typically interdependent so that the stack is always centered on the platform. This arrangement is particularly suited for use with the shortened roller, since the roller will always be centered with respect to the stack.
Machines have comparatively recently been introduced for translating data on sheets into a form usable by computers. These machines generally require precise alignment of one edge of the sheet for reading no matter how large the sheets are. Thus, feeding devices, as described above with two movable guides, are unsuitable for this application, since the positioning of the edges of the sheets is dependent on the size of the sheets.
However, if one of the guides is fixed in position (to position one edge of the sheets independent of size), the position of a short roller will change with respect to the center of the sheets as the size of the sheets changes. In fact, the position of the roller with respect to the center of the sheets may change so much that the sheets will skew or become wrinkled as they are fed.